GPS (Global Positioning System) is an earth-satellite-based electronic system for enabling GPS receivers in ships, aircraft, land vehicles and land stations to determine time and their geographic and spatial position such as in latitude, longitude, and altitude. GPS is an example of a GNSS (global navigation satellite system) and several different such systems exist. Discussion of GPS herein is without limitation to other GNSS and other analogous electronic systems as well as applicable receiver circuits in a variety of telecommunication systems.
It would be desirable to even more accurately, reliably, rapidly, conveniently and economically maintain accurate time, position, velocity, and/or acceleration estimation in a communication device having a satellite positioning receiver (SPR) or other receiver and its clock source.
Current GPS (Global Positioning System) receivers and other positioning and communications receivers are expected to operate in high dynamic range (e.g., a range of 35 db or so) of receive powers from different satellites and other transmitting sources. Even when received signals are strong the wait time to obtain time information (called a time to fix, total time to first fix TTFF, or otherwise) can be undesirably lengthy. Moreover, some positioning receivers such as GPS receivers need to operate in indoor environments and/or for urban canyon environments and otherwise where the dynamic range of receive satellite signal powers is high, typically 25-30 db or more. These challenging environments exacerbate the problems.
A GPS receiver tracks signals from multiple satellites each of which is transmitting GPS navigation data. The receiver decodes (a) the ephemeris and (b) the Satellite Time from the satellite signals, before computing the receiver position. However, ephemeris is sent only once every 30 seconds in GPS, which is problematic for getting faster fixes. Predicted ephemeris (EPT) may be available and in such cases a key factor affecting the time to fix and the position accuracy is the time taken to find the satellite time. The satellite time is transmitted every six (6) seconds, which is still a long time from the point of view of a user.
Further solutions and alternative solutions are desirable to tackle accuracy of time and position obtained, processor real estate and processing burden, as well as power and energy dissipation in lengthy GNSS processing operations, and other problems.